Methylation status of cyclin-dependent kinase inhibitor genes within the transforming growth factor beta pathway in human T-cell lymphoblastic lymphoma/leukemia

DNA hypermethylation of cell cycle (p15 and p16) and apoptotic (p14, p53, DAPK and TMS1) genes in peripheral blood of leukemia patients

Aberrant DNA methylation of tumor suppressor genes has been reported in all major types of leukemia with potential involvement in the inactivation of regulatory cell cycle and apoptosis genes. However, most of the previous reports did not show the extent of concurrent methylation of multiple genes in the four leukemia types. Here, we analyzed six key genes (p14, p15, p16, p53, DAPK and TMS1) for DNA methylation using methylation specific PCR to analyze peripheral blood of 78 leukemia patients (24 CML, 25 CLL, 12 AML, and 17 ALL) and 24 healthy volunteers. In CML, methylation was detected for p15 (11%), p16 (9%), p53 (23%) and DAPK (23%), in CLL, p14 (25%), p15 (19%), p16 (12%), p53 (17%) and DAPK (36%), in AML, p14 (8%), p15 (45%), p53 (9%) and DAPK (17%) and in ALL, p15 (14%), p16 (8%), and p53 (8%). This study highlighted an essential role of DAPK methylation in chronic leukemia in contrast to p15 methylation in the acute cases, whereas TMS1 hypermethylation was absent in all cases. Furthermore, hypermethylation of multiple genes per patient was observed, with obvious selectiveness in the 9p21 chromosomal region genes (p14, p15 and p16). Interestingly, methylation of p15 increased the risk of methylation in p53, and vice versa, by five folds (p=0.03) indicating possible synergistic epigenetic disruption of different phases of the cell cycle or between the cell cycle and apoptosis. The investigation of multiple relationships between methylated genes might shed light on tumor specific inactivation of the cell cycle and apoptotic pathways.

Downregulation of p21 in myelodysplastic syndrome is associated with p73 promoter hypermethylation and indicates poor prognosis

OBJECTIVES

p21 Can both promote and inhibit tumorigenic processes. We explored the role of p21 in myelodysplastic syndrome (MDS).

METHODS

In this study, we analyzed p21 expression and p73 methylation in 88 patients with de novo MDS.

RESULTS

We found decreased expression of the p21 gene in higher-risk MDS compared with lower-risk groups or healthy controls (P < .05). Patients with p73 methylation had lower p21 than those in the unmethylated group (P < .001). Moreover, there was a significantly positive correlation between p73 and p21 expression in MDS (r = 0.436, P < .001). In vitro assays further confirm the role of p73 methylation in p21 expression. Compared with patients with normal expression levels of p21, patients with lower p21 expression levels experienced much higher rates of transformation to acute myeloid leukemia and lower overall survival both in univariate as well as multivariate analyses.

CONCLUSIONS

Our results suggest p21 expression may serve as a new biomarker to predict clinical outcome in patients with MDS.

TGF-β - an excellent servant but a bad master

The transforming growth factor (TGF-β) family of growth factors controls an immense number of cellular responses and figures prominently in development and homeostasis of most human tissues. Work over the past decades has revealed significant insight into the TGF-β signal transduction network, such as activation of serine/threonine receptors through ligand binding, activation of SMAD proteins through phosphorylation, regulation of target genes expression in association with DNA-binding partners and regulation of SMAD activity and degradation. Disruption of the TGF-β pathway has been implicated in many human diseases, including solid and hematopoietic tumors. As a potent inhibitor of cell proliferation, TGF-β acts as a tumor suppressor; however in tumor cells, TGF-β looses anti-proliferative response and become an oncogenic factor. This article reviews current understanding of TGF-β signaling and different mechanisms that lead to its impairment in various solid tumors and hematological malignancies.

Loss of nuclear pro-IL-16 facilitates cell cycle progression in human cutaneous T cell lymphoma

Cutaneous T cell lymphomas (CTCLs) represent a heterogeneous group of non-Hodgkin lymphomas that affect the skin. The pathogenesis of these conditions is poorly understood. For example, the signaling mechanisms contributing to the dysregulated growth of the neoplastic T cells are not well defined. Here, we demonstrate that loss of nuclear localization of pro-IL-16 facilitates CTCL cell proliferation by causing a decrease in expression of the cyclin dependent-kinase inhibitor p27Kip1. The decrease in p27Kip1 expression was directly attributable to an increase in expression of S-phase kinase-associated protein 2 (Skp2). Regulation of Skp2 is in part attributed to the nuclear presence of the scaffold protein pro-IL-16. T cells isolated from 11 patients with advanced CTCL, but not those from healthy controls or patients with T cell acute lymphocytic leukemia (T-ALL), demonstrated reduction in nuclear pro-IL-16 levels. Sequence analysis identified the presence of mutations in the 5' end of the PDZ1 region of pro-IL-16, a domain required for association of pro-IL-16 with the nuclear chaperone HSC70 (also known as HSPA8). HSC70 knockdown led to loss of nuclear translocation by pro-IL-16 and subsequent increases in Skp2 levels and decreases in p27Kip1 levels, which ultimately enhanced T cell proliferation. Thus, our data indicate that advanced CTCL cell growth is facilitated, at least in part, by mutations in the scaffold protein pro-IL-16, which directly regulates Skp2 synthesis.

p53-independent epigenetic repression of the p21(WAF1) gene in T-cell acute lymphoblastic leukemia

The p53 protein is a primary mediator of cellular apoptosis and growth arrest after exposure to DNA-damaging agents. Previous work has shown that the majority of childhood acute lymphoblastic leukemia (ALL) cases express a wild type p53 gene, although the functionality of the p53 pathway has rarely been validated. In the present study, the integrity of the p53 pathway was investigated in a panel of ALL cell lines and xenografts established from direct patient explants in immune-deficient mice. A focused real-time quantitative reverse transcription PCR array of known p53-regulated genes identified p21(WAF1) (CDKN1A) as the highest ranked gene to be differentially expressed between B-cell precursor (BCP)-ALL and T-ALL xenografts following exposure to the DNA-damaging drug etoposide. Lack of p21(WAF1) induction was observed in six of seven T-ALL xenograft lines, as well as primary T-ALL cells following irradiation exposure, despite an otherwise functional p53 response. Repression of p21(WAF1) in T-ALL cells was associated with decreased acetylated H3K9 localized at its promoter compared with BCP-ALL cells, together with increased CpG methylation within the first exon and intron. Although the histone deacetylase inhibitor vorinostat failed to induce p21(WAF1) in T-ALL samples, the combination of vorinostat and the demethylating agent decitabine reactivated expression of the silenced p21(WAF1) gene in the Molt-4 T-ALL cell line. Considering the known anti-apoptotic function of p21(WAF1), our findings have significant implications for the responses of T- versus BCP-ALL cells to chemotherapeutic drugs that induce p21(WAF1).

5-Aza-2'-deoxycytidine (decitabine) can relieve p21WAF1 repression in human acute myeloid leukemia by a mechanism involving release of histone deacetylase 1 (HDAC1) without requiring p21WAF1 promoter demethylation

Decitabine is a potent demethylating agent that exhibits clinical activity against myeloid malignancies. Numerous genes silenced by hypermethylation are reactivated by decitabine through a mechanism involving promoter demethylation with subsequent release of histone deacetylases (HDACs) and accumulation of acetylated histones. Recent studies indicating that decitabine also induces regional chromatin remodeling of some unmethylated genes suggest additional mechanisms of action. Decitabine reactivates unmethylated p21WAF1 in some AML cell lines but the possible occurrence of p21WAF1 methylation in AML in vivo has not been studied in detail and decitabine effects on p21WAF1 chromatin remodeling have not been reported. We found that p21WAF1 mRNA was undetectable in 6 of 24 AML patient samples and 4 of 5 AML cell lines but there was no evidence of p21WAF1 promoter methylation. However, decitabine induced p21WAF1 in AML cell lines KG-1 and KG-1a in association with release of HDAC1 and increased acetylated histone H3 at the unmethylated p21WAF1 promoter. Decitabine effects on p21WAF1 histone acetylation and induction were enhanced by the HDAC inhibitor trichostatin A and were independent of wild type p53. Our findings indicate that decitabine can relieve p21WAF1 repression in AML by a mechanism that involves release of HDAC1 without requiring promoter demethylation. Furthermore, our study provides evidence that combined decitabine and HDAC inhibitor treatment can enhance chromatin remodeling and reactivation of an unmethylated tumor suppressor gene. This latter finding is of relevance to the clinical use of these agents in AML as we found the p21WAF1 promoter to be unmethylated in vivo.